The present invention relates broadly to multi-layer, electrically-conductive tubular polymeric composites and to articles such as hoses and tubing, which may be straight or coiled, constructed thereof, and more particularly to such composites used as core tubes in such articles as hose for use in the delivery of compressed natural gas (CNG) and other fuel, or in other applications requiring some degree of electrical conductivity for static dissipation or electrical grounding.
Thermoplastic tubing and hose is used in a variety of fluid transfer applications. In basic structure, tubing and hoses of the type herein involved typically are constructed as having a tubular, innermost core. In reinforced constructions, the core may be surrounded by one or more outer layers of a fiber reinforcement. The reinforcement, in turn, is protected by a surrounding outermost sheath or cover which may be of the same or different material as the core tube. The cover also provides the tubing or hose with increased abrasion resistance.
The core tube, which may be a thermoplastic material molded or, more typically, extruded from one or more layers of one or more of a polyamide, polyolefin, polyvinyl chloride, ethylene vinyl alcohol, polyurethane, fluoropolymer, and/or a synthetic rubber material such as Buna N or neoprene, may be conventionally extruded, or co-extruded as the case may be, and cooled or cured. In some multi-layer tubing constructions, such as used for fuel line applications, a bonding or tie layer may be incorporated between an inner layer or liner which may be chemically-resistant, and a second layer of a stronger, tougher, and, typically, less-expensive material, such as a nylon, polyamide, or polyurethane, which is used as a reinforcement or cover for the liner. The tie layer, which may be formed as a co- or tri-extrusion with the liner and second layers, is formulated to be compatible chemically with both the material of the liner and the material of the second layer such that a thermal fusion bond may be achieved between the liner and tie layer and the tie layer and second layer to thereby consolidate the tubing into an integral structure. The use of such tie layers dictates the selection of specific materials for the liner and second layer so as to be compatible with the material of the tie layer, or vice versa, and is believed limited to the use of melt processible fluoropolymers such as polyvinylidene fluoride (PVDF) or ethylene tetraflurorethylene (ETFE). Depending upon its material of construction, the tube may be cross-headed extruded on a mandrel for support, or otherwise supported in later forming operations using air pressure and/or reduced processing temperatures.
From the extruder, the tube may be collected on a reel or other take-up device for further processing. As dispensed from the reel or, in a continuous in-line process, taken directly from the extruder, the tube, which may be frozen or otherwise chilled, such as by being sprayed with a liquid and gaseous nitrogen mixture or the like to improve dimensional stability, next may be passed through an applicator for its coating with an outer layer of an adhesive material. The adhesive-coated core tube then may be delivered through one or more braiders or winders which may be used to surround the tube with one or more reinforcement layers of a fibrous material such as a monofilament, yarn, or wire. The reinforcement layers, which may be applied under tension and bonded to the core tube via the adhesive layer, typically may be formed of an interwoven braid or a spiral winding of a nylon, polyester, or aramid yarn, or a metal wire.
Following the application of the reinforcement layer, a second adhesive layer may be applied to bond the reinforcement to the outer cover or sheath. Such cover, which may be applied as a cross-head extrusion or a spiral-wound wrapping, typically is formed of abrasion-resistance polymeric material such as a polyamide, polyolefin, polyvinyl chloride, or polyurethane. Again, the adhesive layer bonds the outer cover to the reinforcement layer.
Tubing and hose for many applications must meet particular governmental or industry regulations and therefore are subject to certain performance requirements. For example, in the case of hoses used in the dispensing or other delivery or conveying of CNG or other fuels, such hoses typically must exhibit a certain degree of electrical conductivity for electrical grounding, static dissipation, or otherwise. In this regard, such hoses may employ a core tube formed of a nylon or other material which is rendered electrically conductive via its loading with carbon black or other electrically conductive particulate filler.
For certain applications, however, specifications call for the use of a small diameter, high pressure hose which is more conductive than those conventionally used, but which is still flexible and compatible with natural gas or other fuels. Such hose, moreover, should have a long service and be economical to produce.
In view of the foregoing, it will be appreciated that hose and tubing constructions for CNG and other fuel conveying applications must exhibit a demanding balance of chemical, physical, and electrical properties. Indeed, as commercial and even, such as in the case of filling CNG/gasoline hybrid vehicles, residential applications for such hoses continue to increase, it is believed that improvements in the construction thereof would be well-received by the industry.